Wire chopper module for EDM system

ABSTRACT

A wire chopper module for processing spent electrode emerging from an EDM system employs replaceable inserts that are also movable relative to the feed path of the electrode. Shifting the position of the inserts relative to the feed path of the electrode allows more than one portion of each cutting edge on the insert to be used. Each insert has more than one cutting edge and can be rotated and re-inserted to present a completely new cutting edge. Removable multi-edge inserts that are repositionable relative to the feed path of the spent electrode permit renewal of the cutting edges of the wire chopper module with increased frequency and reduced cost. The wire chopper module also incorporates a flywheel to increase the movement of inertia of the rotating cutting inserts as an aid in overcoming jams. Sharp cutting edges and increased rotational momentum improve the reliability of the inventive wire chopper module.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/139,478,filed May 6, 2002 now U.S. Pat. No. 6,948,413.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to the processing of used electrodedischarged from an electrical discharge machining (EDM) system and moreparticularly to a wire chopper module for shearing used electrode wireinto many small pieces which accumulate in a relatively dense pile.

2. Description of the Related Art

The process of electrical discharge machining (EDM) is well known. Anelectrical potential (voltage) is established between a continuouslymoving EDM electrode and an electrically conductive workpiece. Thepotential is raised to a level at which a discharge is created betweenthe EDM electrode and the workpiece. The intense heat generated by thedischarge will melt and/or vaporize a portion of both the workpiece andthe electrode to thereby remove, in a very small increment, a piece ofthe workpiece. By generating a large number of such discharges, a largenumber of increments are removed from the workpiece whereby theworkpiece can be cut very precisely to have a desired planar contour. Adielectric fluid is used to establish the necessary electricalconditions to initiate the discharge and to flush debris from the activemachining area.

The EDM process erodes the wire electrode as well as the workpiece.Therefore, EDM systems continuously renew the wire electrode from acoil. Spent electrode wire has previously been allowed to accumulate ina reservoir below the EDM system. This approach proved unacceptablebecause the wire has a tendency for expansion in the reservoir. Thisnecessitates frequent intervention by the operator because the wireforms entanglements, which rapidly fill the space available in thereservoir. It is known to crimp the electrode wire by making it passbetween two toothed wheels or also to cut it into small pieces whichpossess the capability of accumulating in a relatively dense pile. Adevice for cutting the wire into pieces is described in U.S. Pat. No.4,016,395.

A continuing problem with prior art wire-chopping devices is the rapidwear of the tool edges used to section the wire. EDM wire is typicallycomprised of tough metal allows to give it the requisite tensilestrength. Chopping this wire results in high wear to cutting surfaces.If cutting surfaces wear to the extent that the wire is no longerchopped cleanly, the wire-chopping device can jam resulting in a machineshutdown.

Reliable processing of spent EDM electrode is essential to reliableoperation of EDM equipment, for example, at night or over a weekend. EDMsystems frequently require a large capital investment, which motivatesthe owner to keep the machines in use as continuously as possible.Failure of the electrode disposal device results in expensive downtime.The premium placed on reliable electrode disposal has necessitatedfrequent service typically including replacement of portions or theentire wire-chopping device to renew the cutting surfaces.

One prior art wire-chopping device comprises a plurality of bladesmounted to a rotating shaft. A stationary wire guide orifice ispositioned to feed wire into the blades generally transversely to theaxis of blade rotation. The wire is sheared transverse to its feed pathas the blades pass the exit orifice of the wire guide. The blades andwire guide orifice are constructed of tungsten carbide or similarhardened material to increase their durability. The blades arepermanently fixed to a shaft of the wire-chopping device by welding orother known process for fixing a hard cutting edge to a cutting tool.The prior art discloses a wire-chopping device in which the wire guideorifice has two possible locations, each of which guide the spentelectrode into axially spaced portions of the cutting blades. When oneportion of the cutting blade is dulled, the write guide orifice isrepositioned to feed wire toward a fresh cutting surface on the cuttingblades. Once the cutting blades are dulled in both available locations,the prior art wire-chopping device must be removed and discarded orremanufactured by inserting a new shaft with new cutting blades.

The prior art wire-chopping devices of the rotating blade/stationaryanvil type require frequent replacement to renew the permanentlyattached blade cutting surfaces. This results in high expense and thenecessity to maintain an inventory of remanufactured and/or newwire-chopping devices. There is a need in the art for a wire-choppingdevice in which the cutting surfaces can be frequently and inexpensivelyrenewed without necessitating replacement of the entire device.

SUMMARY OF THE INVENTION

Briefly stated, a preferred embodiment of the present inventioncomprises a wire chopper module in which both the stationary androtating cutting tool edges used to shear spent EDM electrode are bothrepositionable and replaceable. Repositioning the cutting edges relativeto the feed path of the spent electrode greatly extends the serviceablelife of each cutting edge by permitting multiple uses of each edge. Whenall the available cutting edges are used, replacement of the cuttingedges is easily accomplished in the field by replacement of an insertcarrying the cutting edge. Thus, cutting edges can be renewed morefrequently and with less expense, resulting in increased EDM systemreliability.

One preferred embodiment of the wire chopper module in accordance withthe present invention comprises a frame that supports a shaft forrotation in bearings. The shaft includes a plurality of longitudinalchannels configured to receive and retain replaceable inserts. Each ofthe disclosed cutting inserts includes two cutting surfaces. The shaftincludes an arrangement for fixing the cutting inserts in alternativepositions along the length of the shaft. A different portion of thecutting edge on the insert is used to shear the wire in each position.In this manner the channel, shaft and replaceable, repositionable,two-edge cutting inserts allow each insert to present four fresh activecutting edges. The inserts are replaceable and repositionable withoutreplacement or extensive disassembly of a wire chopper module inaccordance with the present invention.

A removable anvil holder supports an anvil whose cutting edge cooperateswith the rotating cutting inserts to shear spent electrode transverselyto it feed direction. The anvil holder defines generally conical wireguide orifice that extends from an entrance opening to a smaller exitopening. The exit opening directs the spent electrode over the activecutting edge of the anvil and into the rotating cutting edges of thecutting inserts. A preferred embodiment of the anvil holder includes aslot or opening which receives a removable anvil having a plurality ofcutting edges. The slot or opening is configured to permit movement ofthe anvil relative to the exit opening so that more than one portion ofeach anvil cutting edge is available to shear the spent electrode.

In accordance with the present invention, one preferred embodiment ofthe anvil is configured as a square slab of carbide or hard materialthat is received in the anvil holder in any of eight positions topresent eight new cutting edges before requiring replacement. The anvilis moveable relative to the wire guide orifice exit opening so that eachof the eight cutting edges on the anvil can be used at least twice. As aresult, a wire chopper module in accordance with the present inventioncan utilize the same anvil to present sixteen new cutting edges, greatlyreducing the cost of renewing the stationary cutting edge in theinventive wire chopper module.

A wire chopper module in accordance with the present invention alsoinclude a flywheel mounted to the shaft to increase the moment ofinertia of the rotating shaft and cutting inserts. This increased momentof inertial helps avoid jams that may occur when cutting surfaces becomedull.

An object of the present invention is to provide a new and improved wirechopper module for an EDM system that permits renewal of both therotating and stationary cutting edges without necessitating majordisassembly or replacement of the wire chopper module.

Another object of the present invention is to provide a new and improvedwire chopper module for an EDM system that reduces the cost andincreases the reliability of EDM system operation.

A further object of the present invention is to reduce the cost andcomplexity associated with renewing the cutting edges of a wire choppermodule for an EDM system.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will be apparentfrom the following detailed description, claims and drawings in which:

FIG. 1 is a perspective view of a wire chopper module in accordance withthe present invention;

FIG. 2 is an exploded view of the wire chopper module of FIG. 1;

FIG. 3 is a side view of the wire chopper module of FIG. 1;

FIG. 4 is a sectional view through the wire chopper module of FIG. 3taken along line 4—4 thereof;

FIG. 5 is a side view of a shaft for use in conjunction with the wirechopper module of FIGS. 1–4; and

FIG. 6 is a right end view of the shaft of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIGS. 1–6, wherein like numbers refer to similarparts, one preferred embodiment of a wire chopper module in accordancewith the present invention is illustrated in FIGS. 1–4. The wire choppermodule 100 is inserted in the path of spent wire electrode exiting froman EDM system. The illustrated wire chopper module 100 comprises a frameassembled from a front end cap 22 and a rear end cap 20 that receivefour body pins 30, 30 a. Bearings 24 are received in each of the endcaps 20, 22 to support the shaft 60 for rotation within the frame. Inthe illustrated embodiment, one of the body pins 30 a defines an aid 32for positioning an anvil holder 40.

The anvil holder 40 of the illustrated preferred embodiment 100 ismounted between two of the body pins 30, 30 a. A lower semi-cylindricalcutout 45 on the anvil holder 40 is configured to fit over the body pin30 a at the positioning aid 32. The upper surface 47 of the anvil holder40 is configured to slide under an adjacent body pin 30 and snap intoplace such that the anvil holder is compressively engaged between thetwo body pins. The anvil holder 40 is provided with a jack screw 44 in athreaded bore that serves to jack the upper portion of the anvil holder40 away from its snapped engagement between the body pins 30, 30 a.Driving the jack screw 44 brings it into contact with the body pin 30and pivots the anvil holder 40 out of snapped engagement.

The anvil holder 40 defines a wire guide orifice 42 in the form of aconical opening. The wire guide orifice 42 extends from an entranceopening to a smaller exit opening 43. The anvil holder 40 also defines aslot or opening 49 for reception of an anvil 70. The anvil 70 issupported in the anvil holder 40 with one of the cutting edges on theanvil and a portion of an anvil surface defining a working portion ofthe exit opening 43 in the anvil holder 40. By working portion, it ismeant that this portion of the exit opening 43 acts in cooperation withthe rotating cutting edges to shear the spent electrode (notillustrated).

A preferred embodiment of the anvil 70 is a square slab which can bereceived in any one of eight positions into the slot 49 defined in theanvil holder 40. It will be apparent that each of these eight positionspresents a fresh cutting edge 72 for shearing the EDM electrode as itpasses through the wire guide orifice 42.

As best seen in FIG. 2, the anvil holder 40 is configured tocompressively engage the anvil 70 when the anvil holder is snappedbetween the body pins 30, 30 a. The slot 49 for receiving the anvil 70allows lateral movement of the anvil relative to the exit orifice 43when the anvil holder 40 is not fixed between the body pins 30, 30 a.This lateral movement permits each of the eight cutting edges 72 of theanvil 70 to be used at least two times. Thus, each anvil 70 can berotated and positioned to present at least sixteen fresh cutting edgeportions before requiring replacement.

The shaft 60 in the illustrated embodiment defines four longitudinallyextending channels 62 configured to receive and retain moveable andrepositionable cutting inserts 80. Each of the cutting inserts 80 isconfigured to have two cutting edges 82. When mounted to the shaft 60,one cutting edge 82 is positioned to radially project from the shaft 60while the other cutting edge 82 is received in a channel 62. Thecomplementary cross-sectional configurations (best seen in FIG. 4) ofthe channels 62 and the received cutting inserts 80 allow the cuttinginserts to move longitudinally along the shaft 60. The shaft 60 alsodefines a plurality of radial grooves 66 intersecting the channels 62. Ashaft portion 64 of reduced cross section permits insertion and removalof inserts 80 from the channels 62 without removal of the shaft 60 fromthe frame 20, 22, 30, 30 a.

With reference to FIGS. 5 and 6, the illustrated embodiment of the shaft60 defines four longitudinal channels 62 equiangularly arranged aroundthe circumference of the shaft. The shaft 60 also defines four radialgrooves 66 intersecting the longitudinal channels 62. Channel portionsbetween the grooves 66 interact with the sectional configuration of theinserts 80, as best seen in FIG. 4, to retain the inserts for rotationwith the shaft 60. The radial grooves 66 allow each insert 80 to beretained to the shaft 60 in either of two longitudinal positions 61, 63.Rings 68 disposed in two axially spaced grooves 66 define thelongitudinal positions 61, 63 for the inserts by blocking movement ofthe inserts 80 along the channels 62. Rings placed in grooves A and C(of FIG. 5) define a first position 61 for the inserts 80, while ringsreceived in grooves B and D define a second longitudinal position 63.This arrangement permits each cutting edge 82 on the inserts 80 to berenewed by repositioning the insert 80 so that a fresh portion of thecutting edge 82 is presented adjacent the working portion of the wireguide orifice 42 defined by the anvil 70.

FIG. 4 illustrates the compressed engagement of the anvil holder 40between two of the body pins 30, 30 a. The jackscrew 44 is arranged topush the anvil holder 40 away from one of the body pins 30 and releaseit from this snapped in, compressed engagement. FIG. 4 also illustratesa slit 41 in the anvil holder 40 adjacent the anvil receiving opening49. This slit 41 gives some flexibility to the anvil holder 40 aroundthe anvil 70. When released from between the body pins 30, 30 a, theanvil holder 40 permits removal and/or repositioning of the retainedanvil 70. When installed to the frame, the compressed relationship ofthe anvil holder 40 between the body pins 30, 30 a securely retains thereceived anvil 70 in its selected position relative to the exit 43 ofthe wire guide orifice 42.

In the illustrated embodiment, elastic O-rings 68 are utilized to retainthe received inserts 80 in a selected longitudinal position. It will beunderstood by those of skill in the art that this function might beserved by snap rings, e-clips, O-rings formed of metal coil spring, orthe like. Other configurations for retaining the movable inserts 80 in aselected longitudinal, position are intended to be within the scope ofthe present invention.

From the above description, it will be understood that each anvil 70 canbe repositioned to present sixteen fresh cutting edges and each insert80 can be repositioned to present four fresh cutting edges. The anvil 70and each insert 80 can be replaced without necessitating significantdisassembly of the wire chopper module 100. By significantly reducingthe cost and complexity of renewing the cutting edges of a wire choppermodule, the present invention makes it practical to more frequentlyrenew the cutting edges and thereby increase the reliability of EDMequipment incorporating the inventive wire chopper module.

The illustrated embodiment for a wire chopper module 100 in accordancewith the present invention also includes a flywheel 50 fixed to theshaft 60. The flywheel 50 increases the rotational inertia of the movingparts of a wire-chopper in accordance with the present invention. Thisincreased inertia allows the inventive wire chopper module 100 to avoidmany of the jams that may have occurred in prior art wire-choppers asthe cutting surfaces became dulled. A jam that is avoided preventsstoppage of the EDM system and increases productivity.

While a preferred embodiment of the foregoing invention has been setforth for purposes of illustration, the foregoing description should notbe deemed a limitation of the invention herein. Accordingly, variousmodifications, adaptations and alternatives may occur to one skilled inthe art without departing from the spirit and the scope of the presentinvention.

1. A chopper module for shearing wire into numerous discrete sections, said chopper module comprising: a shaft carrying a plurality of cutting edges and rotatable about an axis of rotation generally perpendicular to a feed path of the wire; and an anvil holder defining a wire guide orifice extending from an entrance to an exit having a circumference and an anvil-receiving slot for holding a removable anvil, said anvil comprising a plurality of cutting edges, a portion of one of the cutting edges defining a working portion of the circumference of the exit, said anvil laterally moveable in said anvil holder relative to said exit so that at least two different portions of each cutting edge can define the working portion of the circumference of the exit, wherein said anvil holder engages said anvil to fix said anvil in a selected position relative to the circumference of the exit and wire fed through the wire guide orifice emerges from the exit and is sheared generally transversely to the feed direction between the shaft-carried cutting edges and the working portion of the circumference of the exit.
 2. The chopper module of claim 1, wherein the anvil is configured as a slab having parallel opposed first and second square faces and said anvil is receivable in the anvil holder so that at least one portion of each of the four edges of the first and second faces is positionable to define the working portion of the circumference of the exit.
 3. The chopper module of claim 1, comprising: a frame supporting the shaft for rotation, wherein the anvil holder is mounted to the frame and engagement of the anvil holder with the frame compresses the anvil holder against said received anvil to fix the anvil in a selected position relative to the circumference of the exit.
 4. The chopper module of claim 1, comprising a flywheel fixed to said shaft for rotation therewith.
 5. A chopper module for shearing wire into numerous discrete sections, said chopper module comprising: a shaft carrying a plurality of cutting edges and rotatable about an axis of rotation generally perpendicular to a feed path of the wire; a frame supporting the shaft for rotation; and an anvil holder defining a wire guide orifice extending from an entrance to an exit having a circumference and holding a removable anvil in fixed position relative to the rotating shaft, said anvil comprising a plurality of cutting edges and positioned so that a portion of one of the cutting edges defines a working portion of the circumference of the exit, wherein the anvil holder defines an anvil-receiving slot, the anvil holder is mounted to the frame and engagement of the anvil holder with the frame compresses the anvil holder against said received anvil to fix the anvil in a selected position relative to the circumference of the exit. 